1. Field of the Invention
A method of avoiding monitoring useless dynamic scheduling information (DSI) of a multimedia broadcast multicast service (MBMS) in a wireless communication system and related communication device is provided, and more particularly, a method of avoiding monitoring useless DSI for a user equipment when the UE receives intermittent services or short session services and related communication device is provided.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. The 3GPP is now involved in the further advancements for E-UTRA and proposes an LTE-Advanced system as an enhancement of the LTE system. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs). The LTE protocol stack can be segmented into access stratum (AS) layer and non-access stratum (NAS) layer. The AS layer includes sublayers as Layer 3, also known as the Radio Resource Control (RRC) layer, Layer 2, consisting of three sub-layers that are the Packet Data Convergence Protocol (PDCP) layer, the Radio Link Control (RLC) layer, and the Medium Access Control (MAC) layer, and Layer 1, also known as the Physical (PHY) layer. The NAS layer processes the signaling between the UE and the core network.
Evolved multimedia broadcast multicast service (E-MBMS) has been introduced in the LTE specification to broadcast or multicast TV, films, information such as free overnight transmission of newspaper in a digital form. Two important scenarios have identified for the E-MBMS: one is single-cell broadcast, and the other is E-MBMS single frequency network (MBSFN). The MBSFN is a simulcast transmission technique that realizes transmission of identical waveforms at the same time from multiple cells covering a geographic area called an MBSFN area. To realize E-MBMS, the PHY layer of the LTE system offers information transfer services between a physical multicast channel (PMCH) and a downlink transport channel called multicast channel (MCH). The MCH is required to be broadcasted in the entire coverage area of each cell in the MBSFN area. Scheduling of each MCH is done by a multicast coordination entity (MCE), which can be a part of a network except the E-UTRAN. The MAC layer of the LTE system offers data transfer services between the MCH and logical channels including a multicast traffic channel (MTCH) and a multicast control channel (MCCH), which are point-to-multipoint channels for transmitting traffic data and control information. MCCH is transmitted every MCCH repetition period and MCCH may change in a MCCH modification period, in which the same MCCH information may be transmitted a number of times.
The MBSFN transmission takes place on dedicated subframes referred to as MBSFN subframes. Within MBSFN subframes, the transmission of a specific MCH carrying MTCH occupies a pattern of subframes which are not necessarily adjacent in time, called MCH subframe allocation pattern (MSAP). The MSAP for every MCH carrying MTCH is signalled on the MCCH. The MSAP occasion comprises a set of subframes defined by the MSAP during a certain period. A UE determines what subframes are used by each MTCH in the MSAP occasion according to a dynamic scheduling information (DSI), which is generated by the eNB and allocated in the first subframe of the MSAP occasion. The DSI includes values as stop indications for indicating the last subframe of each MTCH. Except the values used as stop indications of MTCH, there are several values reserved for further usage. When an MBMS service is ongoing, one or more sessions are sequentially generated with respect to the corresponding MBMS service.
For an intermittent service which has the updated frequency in a range of tens of seconds or even minute, like a news ticker or a stock ticker, it may only have one active MBMS session in several MSAP occasions. If a UE only subscribes to this kind of service, the UE still needs to wake up to receive DSIs according to the MSAP periodicity even though most of times the received DSIs includes no scheduling information for the intermittent service. These periodical wakeups consume UE power with no any actual gain.
For a short session service, like file download, the actual transmission may be much shorter than the MCCH modification period, which is 5.12 seconds or 10.24 seconds in the current specification. Since there is no session end notification, a UE cannot stop monitoring DSI until a next MCCH modification period. A UE may monitor DSI for receiving a short session service at all MSAP occasions in a long MCCH modification period, such as 10.24 seconds, and find MBMS sessions in MSAP occasions of only 1 second, which indicates that 90% of the DSI monitoring is fruitless and wastes power.